Wastewater that is generated from within a building will leave the building by force of gravity and be fed into the gravity main. From the gravity main it will continue to the nearest wastewater treatment plant.

If the treatment plant cannot be reached by gravity alone, because either the treatment plant is too far away or it is uphill from the source of wastewater, then the wastewater will flow towards a sewerage pump station where it will be pumped to the next gravity main or directly to the wastewater treatment plant.